Michael Ragland  wrote:

> Species- One kind of organism. Of sexually reproducing organisms, one or
> more natural populations in which individuals are interbreeding and are
> reproductively isolated from other groups.
> 
> 
> Is this a sufficient definition of species? I've been reading some of
> the controversy over this term and as far as I can see this is an apt
> definition of biological species. It doesn't take anybody with a little
> general knowledge of Darwinism and embryology that we were once
> "different" species. Over a long gradual period of time we
evolved from
> other life forms or "species". If one sticks to our current definition
> of species I think there is no contadiction with evolution. However,
> strictly in terms of evolution the term "species" is fluid and ever
> changing. There is no question, assuming we don't destroy ourselves,
> that in a billion years we won't resemble anything like what we do now
> in terms of internal and external morphology. Nevertheless, as
> incredible as it may seem there will likely be vestiges of us remaining
> a billion years from now...to use an analogy like the human embryo at a
> certain early stage briefly resembles or is like a fish. 
> 
> There is no question evolution can be externally influenced by future
> genetic engineering and this in itself will be a new form of evolution.
> Natural selection won't be controlled but will be gradually influenced
> and at some point in the far off future replaced completely by
> artificial selection via genetic engineering. 
> 
> Does everybody agree with the aforementioned definition of species? Do
> people agree on an evolutionary scale the term and meaning is fluid and
> subject to change?
> 
> Michael Ragland

There are around 25 distinct "definitions" of the category
"species" in
the literature at present. The biospecies definition has been criticised
a lot, and there are a number of "isolation" conceptions in play. One of
the problems with it is that it is a synchronic, or "time-slice" concept
that fails over any length of time and sometimes over geographic
distance, and it is rarely operational in diagnosis.

Evolution conceptions of species tend to follow Simpson's "lineage with
a unique evolutionary fate and tendencies", while phylogenetic concepts
fall either to "autapomorphies" (unique constellations of characters
that all and only that species' members bear), or to a species being
merely the terminal node on a phylogenetic tree. There are genetic
definitions such as Templeton's cohesion conception, and so on.

Each of them has their own problems. I recommend you get hold of Jody
Hey's (2001). Genes, concepts and species: the evolutionary and
cognitive causes of the species problem. New York, Oxford University
Press. It will introduce you to many of the issues. If you would like to
look at some of the questions regarding speciation, try

Schilthuizen, M. (2001). Frogs, flies, and dandelions: the making of
species. Oxford, Oxford University Press.

Do a web search for "James Mallet" and you should locate an essay o fhis
on the species concepts (I add a couple and reject one of his, but it's
damned good as it stands).
        
-- 
Dr John S. Wilkins, www.wilkins.id.au
"I never meet anyone who is not perplexed what to do with their
 children" --Charles Darwin to Syms Covington, February 22, 1857
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